1. Field of the Invention
The present invention relates to an ink jet recording head in which ink droplets are formed by jetting the ink through ink discharge orifices.
2. Related Background Art
An ink jet recording head of this type was described in, for example, Japanese Laid-open Patent Application No. 54-51837, wherein an ink jet recording method thereof has a different feature from other ink jet recording methods in that the motive force for the discharge of ink droplets is obtained by applying heat energy to the ink.
The recording method as disclosed in the above application is characterized in that the ink subjected to the heat energy is heated to produce bubbles adhering to a recording medium to record the information.
A recording head according to this recording method generally comprises ink discharge orifices provided to discharge ink droplets, liquid channels in communication with ink discharge orifices, each having a heat acting portion in which the heat energy useful for the discharge of ink droplets acts on the ink, a heat generating resistive layer for use as electricity-heat converters which is generating means of the heat energy, an upper protective layer for protecting the heat generating resistive layer from the ink as well as a heat storing layer for storing the heat energy, and a support substrate for supporting the whole recording head. Note that the upper protective layer may be omitted.
The heat storing layer, which is provided bwtween the substrate, and the heat generating resistive layer, requires the insulating property particularly when the substrate is electrically conductive. Typically, the heat storing layer is formed by covering the surface of the substrate with an insulating material.
Herein, it is noted that the heat storing layer also serving as an insulation layer requires a poor heat conductivity and an insulating property. Also, it must withstand high temperatures above 600.degree. C., which is a temperature of the heat generating resistive layer when energized, as it will be placed adjacent the heat generating resistive layer to prevent heat radiation to the support substrate. Further, it requires to have an excellent surface property, because it has some influence on the surface property of the heat acting portion which causes ink bubbles to be produced.
Accordingly, an inorganic insulating material, as the material for the heat storing layer meeting the above requirements, has been formed as the film on the surface of the substrate, by chemical vapor phase reaction such as CVD, or vacuum film formation such as PVD.
On the other hand, the material for forming the support substrate on which such heat storing layer is formed as the film, includes preferably those having a great heat conductivity and an excellent surface property, for which a silicone substrate has been conventionally used. However, since the silicone substrate is expensive, and unfavorable in the respect of industrial economy, numerous inexpensive alternative materials have been examined. Thus, inexpensive metallic substrates with great heat conductivity and excellent surface property have been noted. Among them, aluminum which is cheap and has a great heat conductivity has been particularly noted.
However, when the heat storing layer having a thickness of 1.0 .mu.m or more was formed as the film on the metallic substrate by CVD or PVD as above cited, there often occurred some peeling of the heat storing layer from the substrate. When the film thickness is below 1.0 .mu.m, no peeling of the heat storing layer occurs, but the heat storing layer for use with the ink jet recording head as previously described requires a thickness of 1.0 .mu.m or more, preferably, about 3.0 .mu.m, for the purpose of heat storage. Therefore, it was sought that the heat storing layer having a relatively great thickness was constituted so as not to cause any peeling.
The present inventors have discovered as a result of effortful researches that the substrate temperature when forming the film of heat storing layer may have some effects on the peeling of the heat storing layer. That is, when an inorganic insulating material is formed as the film on the metallic substrate by CVD or PVD, the substrate temperature in forming the film is as high as from about 200.degree. C. to 600.degree. C., and when the temperature is decreased from this state down to room temperature, there will occur remarkably a stress due to a difference between thermal expansion coefficients of the metallic substrate and the heat storing layer of inorganic insulating material, because the thermal expansion coefficient of the metallic substrate is larger than that of the silicone substrate. And when this stress becomes larger than a bonding force between the support substrate and the heat storing layer, a peeling of the heat storing layer will occur. In particular, this stress becomes greater with a larger film thickness of the heat storing layer. This phenomenon will occur on almost all the metallic substrates.
Also, the peeling of the heat storing layer due to this thermal stress can also occur when an ink jet recording head having a plurality of energy elements arranged at high density is continuously driven.
A solution for the above problem includes decreasing the substrate temperature when forming the film of heat storing layer, but is unfavorable because if film formation is made at low temperatures, the film quality may degrade such as lower dielectric strength.
Also, no formation materials of the heat storing layer are currently found which meet the insulating property, low heat conductivity, and heat resistance, as well as having a heat expansion coefficient equivalent to that of metal.